It doesn't take advantage in the way you say because you get paid along the same lines. If you bet an accumulator with 2 selections at evens, you get paid at 3/1. (4.0 decimal odds) so that is "fair".

It's profitable for bookies because they have a house edge, and that edge is increased the more subsequent bets you make. The house has more edge with an accumulator than a single bet.

People like to do accumulators because it's more meaningful to win large amounts occassionally than more regularly win less meaningful amounts.

So it's a "trick" to simply increase gambling.

If you had to pick out 8 evens shots in sequence and intended to roll over your bet each time it would have the same effect / outcome, but starting with a pound by the last bet you're effectively placing a 128 quid bet on an evens money.

It's not that the player thinks that they have a better chance of winning than 1/256 it's that it effectively forces them to gamble a lot larger amount in the situations where only 7 out of 8 of their picks come in.

And that's before considering the edge. If we consider that these are probably events that happen more like only 45% of the time (at best) then instead of a 255/1 shot we're looking at 600/1 shot.